Microfabrication, Characterization, and Cold-Test Study of the Slow-Wave Structure of a Millimeter-Band Backward-Wave Oscillator with a Sheet Electron Beam

In this paper, the results of the microfabrication, characterization, and cold-test study of the previously proposed truncated sine-waveguide interaction structure with wideband-matched output couplers for the millimeter-band backward-wave oscillator (BWO) driven by a high-current-density sheet electron beam are presented. Computer-numerical-control (CNC) micromilling was used to fabricate the designed interaction structure. The first sample was microfabricated from an aluminum alloy to test the milling process. The final sample was made from oxygen-free copper. Scanning electron microscopy (SEM) and optical microscopy were used to investigate the morphology of the microfabricated samples, and stylus profilometry was used to estimate the level of the surface roughness. Cold S-parameters were measured in Q- and V-bands (40–70 GHz), using a vector network analyzer (VNA). Using the experimentally measured phase data of the transmitted signal, the dispersion of the fabricated interaction structure was evaluated. The experimentally measured dispersion characteristic is in good agreement with the numerically calculated.